Fools. They left it unencrypted because they wanted everyone to discover kernels, so they can patch it in their next update, its what they did last year, its what they are doing now, i know this because i work for them :D

It makes sense because the kernel doesn't hold user data. Not encrypting it allows faster performance. It also allows a wider group of people to discover potential flaws, and therefore, quicker patches.

Yeah it was a mistake, there's no way Apple would have done that on purpose. The reason it took them a couple days to make a statement was because they had to come up with a reason that would make it plausibly, but if that reason was true, they would have said that right away instead of waiting 2-3 days